Prior art which is related to this technical field can e.g. be found in specifications describing radio frequency duplexer.
The following meanings for the abbreviations used in this specification apply:    3GPP 3rd Generation Partnership Project    BS Base Station    DC Direct Current    FDD Frequency Division Duplex    HSDPA High Speed Downlink Packet Access    LNA Low Noise Amplifier    LTE Long Term Evolution    PA Power Amplifier    Rx Receiver    RF Radio Frequency    TDD Time Division Duplex    Tx Transmitter    WCDMA Wideband Code Division Multiple Access
In present wireless communication systems, frequency-division, time-division, and/or code-division are used to divide the transmitted signal from the received signal. The increasing demand for high speed and spectral efficiency communication impels the development of full-duplex techniques for such communication systems. The common techniques employed are TDD and FDD, which separate the transmission channel and receiving channel in different time slots and in different frequency bands, respectively.
A more challenging technique relies on enabling transmitting and receiving signals at the same time and at the same frequency, with low self-interference from the transmitted signal to the received signal, resulting in full-duplex transceiver for both the base station antenna and the mobile phone antenna.
The main problem of the full-duplex system is the presence of the self-interference caused by the transmitted signal, which can be as large as 25 dBm (316 mW), to the received signal, which can be as small as −90 dbm (1 pW). Thus, the interference can easily saturate the receiver.